The conventional power control device of a lighting fixture, as shown in FIG. 1, is generally comprised of a power switch 23, an electronic ballast 10 and an external lighting power dim control switch 27. The electronic ballast 10 is comprised of a filter 11, a rectifier 13, a power factor controller 15, a logic controller 17, an oscillator 19, and a protection circuit 18. The filter 11, the rectifier 13, the power factor controller 15, the logic controller 17 and the oscillator 19 are connected in series between the power switch 23 and the lighting fixture 20 to form a power supply circuit. The protection circuit 18 is connected between the output end of the oscillator 19 and an input end of the logic controller 17. In order to meet different lighting intensity requirements, a lighting power dim control switch 27 shall be used and connected to the electronic ballast 10 by an additional electric wire. The lighting power dim control switch 27 is controlled by the user to provide a lighting power control signal to the logic controller 17 of the electronic ballast 10, causing it to change the output voltage of the power factor controller 15 or the output frequency of the oscillator 19, so as to further change the impedance of an inductor or the like, and therefore the intensity of light of the lighting fixture 20 is regulated. However, because an additional circuit is required to connect the lighting power dim control switch 27 to the electronic ballast 10, the electric wiring of the lighting system is complicated. Furthermore, because this lighting power control method is achieved by controlling variable resistance, variable inductance, or output frequency, much energy is lost during the transmission of electric power.